Preparation of phenol-ligninaldehyde resins



Patented May 12, 1942 PREPARATION OF PHENOL-LIGNIN- ALDEHYDE RESINS Carroll A. Hochwalt, Dayton, and Mark Plunguian, Chillicothe, Ohio, assignors to The Mead Corporation, Chilllcothe, Ohio, a

corporation of Ohio No Drawing. Original application April 9, 1936,

Serial No. 73,517., Divided and this appllcation June 3,1939, Serial No. 277,320

3 Claims.

This invention relates to the production and use of resinous materials in molding.

It is a principal object of theinvention to provide an inexpensive resinous material containing lignin and having the properties of being quickly and easily molded, the molded products possessing high strength, being very hard, and having substantial resistance to solvents and the like.

It is a further object-to provide as a new prod-' not for molding purposes a condensation product of lignin which has good strength, water resistance, appearance, etc., and which can be readily molded with filler material to produce molded products.

It is a further object to provide a condensation product of lignin for use in molding having the property to cure quickly during the operation.

It is a further object to provide a simple and eflective method for making such lignin products.

Other objects will be apparent from the description and the appended claims.

This application is a division of co-pending application SerI No. 73,517, filed April 9, 1936 Patent No. 2,168,160.

The present invention relates to and is part of a recent development in the field of production and utilization of lignin material, for use in the field of molding. Lignin material is obtained from woody fibrous material and comprises the principal non-cellulosic constituent of the original wood. It may be segregated in different ways, and is conveniently recovered in commercial operations from the spent digestion *liquor resulting from the chemical cooking treatment of therethrough until a predetermined pH value of approximately pH: to pH: is obtained following which the suspension is brought to a temperature of about 50 to 70 C. to cause coagulation and agglomeration of the precipitated particles and to facilitate filtering. The suspension is then cooled to substantially room temperature and filtered,

the filtrate being returned to the recovery system, and the precipitate comprising the desired acid. A lignin material obtained in this manner molding wood in the making of paper. Different chemical processes are used, both acid and alkaline cooks, but for the practicing of the present invention it is preferred to use the spent digestion or black liquor resulting from the alkaline soda or sulfate processes. Such spent liquor is available in large quantities and the lignin can be recovered therefrom quite inexpensively so that such liquor constitutes a preferred source for obtaining a low cost lignin material suitable for. use in this invention. A preferred method of recovery of lignin material from'sp'ent digestion liquor of this character is described in application of Herman J. Reboulet Serial No. 734,425, filedJuly 9, 1934, and in the Joint application of Carroll A. Hochwalt and Richard C. Camp Serial No. 46,- 777, filed October 25, 1935, both assigned to the same assignee asthis application. In that process a black liquor is subjected to a controlled carbonation by passing C02 containing gas separated fraction containing the lignin solids is washed with water and then treated with willcient strong acid such as sulfuric acid to efiect neutralization and removal of any remaining sodium organic compounds. final wash with water to remove any remaining from an alkaline liquor is substantially free of alkaline solvents such as caustic solution, is of such character that it is adapted to be readily molded with fillers, is low in ash, and has a rela-. tively low melting point of not more than approximately C. to 200 C. such that it can be readily fiuxed on hot milling rolls, forming a blanket on the rolls when mixed with fillers and with other resinous substances. I

In accordance with the present invention lignin material having these characteristics is caused to undergo'a condensation reaction preparatory to the preparation of a resinous material ior use in molding. This is efiected by bringing the lignin into contact with those materials,

and under the conditions favorable to the progress of a condensation reaction. This may be done by heating the lignin in the presence of a phenolic body such as phenol, cresol, cresylic' acid, tar acid, or the like and with or without the presence of aldehydic material such as formaldehyde, paraformaldehyde, furfural, hexamethylenetetramine, or the like. This reaction is carried out under suitable conditions such as in an open dish and heated on a steam bath.

These is further preferably used a catalytic agent adapted to facilitate the condensation reaction which may be either an acid material or an alkali. Satisfactory results have been secured using caustic soda, and using hydrochloric acid,

but other well known catalysts as usedin the each other. For this purpose the lignin is first preferably dissolved in phenol or in the other phenolic body. This maybe accomplished by It is then given 'a heating the lignin on a steam bath in the presence of the phenol in an open casserole or dish and stirring. It is found that in this way the lignin may be brought into solution in the phenol quite readily. Air dried lignin may be dissolved in the phenol, or if desired the step of drying of the lignin may be eliminated and it may be mixed with the phenol in its wet condition as originally obtained. For example satisfactory results have been secured by mixing the ligninas obtained in accordance with the processes described above with phenol, the lignin containing approximately 80% by weight of water.

The lignin solution in phenol is then mixed with the aldehydic body; this may be conveniently accomplished by adding formaldehyde solution to the lignin solution and stirring the two solu-,

tions to thoroughly mix the same together. By

first dissolving the lignin in the phenol, and thereafter effecting a mixture of the aldehyde solution with the solution of lignin, a very thorough and complete intermixture is assured of the lignin with both the phenolic and aldehyde bodies so that a condensation of the lignin itself is facilitated and more uniform results secured thereby.

The heatingis then continued with frequent powder. This powder was then placed in the mold and molded at a temperature of 330 F. and a pressure of 2500 pounds per square inch. After a curing time of 60 secondsthe reaction was complete and the mold released, with the production of a strong hard-surfaced, dense and well-cured article. The time of cure is a factor of economic importance in commercial operations and it is highly desirableto obtain as short a curing time as possible. And in accordance with the present invention very limited curing times are required, in some instances being materially less than that indicated above.

In the practicing of the invention on a commercial or plant scale it is preferred to substitute for the open dish an autoclave of usual character within which the material may be subjected to controlled pressure above or below atmospheric during the reaction process. stirring mechanism is provided and samples may be taken periodically to test and determine the extent of the reaction.

The proportions of the materials as used in the condensation reaction may be varied over stirring of the mixture until the reaction has advanced sufllciently for the purpose desired. It

-is found that as the reaction is continued the mass begins to show evidences of solidifying, and the reaction should be stopped by discontinuing the'heating at the point which will produce a condensation product having the desired plastic characteristics.

The following has been developed as a convenient method of determining how far the reaction should be allowed to proceed in order to get-a resinous product suitable for use in subsequent molding operations with a fibrous or other filler material. As the mass solidifies it is tested with a weight of predetermined massand maving a predetermined surface area, and the reaction is continued until the mass will just sup-- port such a weight upon its surface. As an 11- lustration of such a test which has been found to give satisfactory results, a 25 gram weight having a diameter of 22 mm. has been used in the manner described above. Is will be understood however that this is given as illustrative only.

. customary apparatus, and will give good results as to length .of cure required in the production of molded articles. As a specific example, the above resinous material was mixed dry with an equal quantity by weight of fibrous 'filler and the mixture then passed between the nip of a pair of smooth rolls heated to a temperature of about 230 F. As the resin binder materials fiuxed a blanket was formed about the rolls, the

blanket being doctored off and the sheet repassed through the. mill as required to produce the desired degree of preliminary setting up of the resins, and the uniform envelopment and impregnation by the resins of the particles of filler. The resulting sheet was then broken and ground up to fine powder form to provide the molding a considerable range in accordance with the characteristics of the product desired. As an examplelignin may be used with substantially equal quantities of phenol and formaldehyde. In one operation good results were secured utilizing 25 parts of lignin material, 25 parts of phenol, and 34 parts of a 40% formaldehyde solution. The proportion of aldehyde may be varied and satisfactory results have been obtained using quantities of formaldehyde varying from 17 parts in the above formula to 50 parts. Similarly the proportion of lignin and phenol may be varied as desired, it usually being desirable to use as large a quantity of lignin aspossible because of its cheaper cost than phenol.

The present process is further characterized by very satisfactory yields, making the practicing of the invention highly economical. For example in the composition described above using 25 parts of lignin, 25 parts of phenol and 34 parts of 40% formaldehyde, including 2 parts sodium hydroxide, a yield of approximately 64.5 parts of resinous molding material was obtained. Similarly using .the same ingredients with an increase in the quantity of formaldehyde to 50 parts, a yield of about 71 parts, very close to the maximum theoretical yield was obtained.

The catalyst used to further the condensation reaction may be either an acid or an alkaline material, although better. results in the utilization of lignin obtained by the process of the above referred to copending application have been secured by the use of an alkaline catalyst. For example in the composition just described two parts of sodium hydroxide were used; alternately one part of an acid such as hydrochloric acid can be used. The catalyst is" added to the other ingredients and is present during the heating on the steam bath.

digestion liquor, or as a purified lignin derivative thereof, the resulting product was found to be unsatisfactory. Where a condensation reaction was carried out including suchlignin ma terial and phenolic and aldehydic bodies, and the reaction was allowed to proceed so far that Also mechanical Where the resulting resin became brittle upon cooling,

' stiff to mold after hot-milling.

It has been found that lignin as obtained from the sulfite waste liquor may however be subjected 'to such controlled processing as to free it of the objectionable sulfonic acid radicals and convert itv into a form capable of producing results comparable with those secured with a lignin obtained from black liquor. This has been accomplished by digesting the non-alkaline lignins (such as the sulfite) with caustic soda, and lignin material having satisfactory char teristics as to condensation and formation of moldable powders etc. has been obtained from.

sulfite lignin in this way. I

In such processing the sulfite liquor, preferably concentrated to approximately 50% is treated with caustic soda and subjected to elevated tem-' perature and preferably to pressures above at- Inospheric. Thus when treated with 15.7% NaOH at atmospheric'pressure and at a temperature of 105 C., a yield of lignin product amounting to approximately 12% by weight of the concentrated liquor was obtained, the lignin having a melting point and other characteristics comparable with those found in lignin from the alka-. line processes.

As another example, the concentrated liquor was treated with 7.2% NaOH at av temperature of 233 C. and a pressure of 420 lbs. per sq. in. This resulted in a higher yield of the order of 25% of the concentrated liquor, of lignin mate-[ rial of generally similar characteristics.

When a sulfite lignin from which the carbohydrates had been removed (known commercially as Maratan extract) was digested with 6.8% NaOH at 245 C. and 525 lbs. per sq. in., a very satisfactory lignin material was obtained having a melting point of the order of 90 C., and capable of being readily molded similarly to the molding of a lignin originallysecured by an entirely different process.

In each of these cases the altered lignin matewith the usual fillers. It is available inexpensively, and can be utilized in accordance with the present practice in the molding field, since it does not require the existence of unusual conditions during the molding operation. And the molding cycle including the time of cure of the molded article is sufliciently short to be comparable with the practice in this art. Also the method herein described for obtaining this product is extremely simple and can be readily carried out with different specific in redients to'obtain molding products as described.

While the process and product herein described constitute preferred embodiments of the invention, it is to be understood that the invention-is not limited to this precise process and product, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. The method of preparing a water-resistant thermosetting resinous material for use in molding which comprises recovering lignin solids from black liquor of alkaline reaction in a condition substantially free of alkaline solvents and sodiumorganic compounds and subjecting such lignin solids as thus recovered and following separation from alkaline solution to a condensation reaction by heating said lignin solids in the presence of a phenolic body and an aldehydic material to provide a potentially reactive thermosetting resinous material.

2. The niethod of forming a potentially reactive water-resistant thermosetting resinous material of the character described which comprises separating lignin solids from black liquor to provide said lignin material in a form substantially free of alkaline solvents and sodium organic com pounds, dissolving said lignin solids as thus separated in a phenolic body, and reacting said solution with an aldehydic material under heat in the presence of a catalyst adapted to promote a condensation reaction.

3. The method of forming a potentially reactive water-resistant thermosetting resinous material of the character described which comprises recovering lignin material from black liquor of alkaline reaction and separating such lignin material from alkaline solvents to provide separated lignin solids substantially free of alkaline solvents and sodium organic compounds, dissolving such lignin solids as thus separated in a phenolic body, and reacting said solution with an aldehydic material under heat in the presence of a small quantity of a catalyst adapted to promote a condensation reaction.

CARROLL A. HOCHWALT.

MARK PLUNGUIAN. 

